But a critical report for the UN in 2005 said the system became corrupt, because Saddam Hussein’s regime demanded “kickbacks” from foreign firms in return for the contracts.

An Eli Lilly spokesman said: “We were asked to supply documentation in mid-December. We are compiling these documents and they will be sent to the SFO in the new year.”

A spokesman for GlaxoSmithKline added: “GSK does not believe that its employees or its agents in Iraq knowingly engaged in wrongdoing regarding the oil-for-food programme.

“In fact GSK went to considerable lengths to co-operate with UK Government authorities responsible for the UK administration of the programme, and to impose anti-corruption measures when dealing with intermediaries in Iraq at a time when the environment was extremely volatile and difficult.”

And an AstraZeneca spokeswoman said: “AstraZeneca has received a request from the Serious Fraud Office for documents as part of its review of the oil-for-food programme in Iraq. The company will be providing the documentation.”